I have not heard of this tradition, so I looked it up and found an interesting article about it. Evidently, in the Ovahimba and Ovazemba tribes of Northern Namibia, this is still common. And in fact, if a visitor comes with his wife, the two men may trade wives for a night. The article says that the women do not have a problem with it! Wow. Interesting topic for a short story, @raymonpeter.